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Hidden Audio

Approach the Boss of Opposing Force to hear backwards audio composed of the
phrase "To win the game you must kill me Randy Pitchford" when played correctly.
Randy Pitchford is the leader of the development team at Gearbox Software.

Original Levels

You can play all the Half-Life levels that Gordon Freeman went through as Adrion
Shepard, but in the lab none of the scientists will talk to you.